Service-observing set



G. CRISSON.

SERVICE OBSERVING SET.

APPLICATION FILED NOV: 24. 1920.

1,412, 103. Patented Apr. 11, 1922.

UNITED STATES PATENT orrics.

GEORGE CRISSON, OF HACKENSACK, NEW JERSEY, ASSIGN'OR T0 AMERICAN TELE- PHONE AND TELEGRAPH COMPANY, A CORPORATION OF NEW YORK.

SERVICE-OBSERVING SET.

Specification of Letters Patent.

Patented Apr. 11, 1922.

Application filed November 24, 1920. Serial No. 426,271.

To all who 1a it may concern.

Be it known that I, GEORGE CnrssoN, residing at Hackensaek, in the county of Bergen and State of-New Jersey, have invented certain Improvements in Service-Observing Sets, of which the following is a specification.

This invention relates to communication systems and more particularly to arrangements for observing the service on such systems.

In general, it is the purpose of the invention to provide a service observers set, or listening in apparatus, which is adapted to be used simultaneously with a plurality of circuits and which may be associated with such circuits in a manner so that there will be no interference, such as cross-talk, between said circuits. Furthermore, with the arrangements of this invention a considerable reduction in apparatus may be eilected. Other objects and purposes of the invention will appear more fully from the detailed description hereinafter given.

In the arrangements of this invention, the operators listening set, or service observing set, is associated with the output circuit ot a device, such as an amplifier, having a substantially infinite input impedance. Any type of device or amplifier might be used which would have substantially infinite in put impedance and would require very little input energy for its operation and would absorb a negligible amount of energy "from the line. The well-known vacuum tube amplifier is a. suitable device for use in this connection. In the input circuit of the amplifier there is provided a separate transformer for each circuit upon which service observation is to be made at the same time. The line windings of each of these transformers are bridged across the corresponding line, while the secondary windings are connected in series in the grid circuit of the vacuum tube amplifier. The observing operator an then listen to what is taking place upon all of the circuits at once and no interference between the talking circuits will be produced, since the grid circuit of the vacuum tube has a substantially infinite impedance and no current will flow through any of the input transformers due to voltages set up in any other input transformer.

The invention may be more fully understood from the following description of its operation and by the accompanying drawing in which is illustrated a preferred form ot the invention. In the drawing there is shown a plurality of transmission circuits such as l and 2. A service observers arrangement, or listening in device, is shown associated with these circuits. The listening in device comprises an operators receiver 10 associated through the transformer 9 with the output circuit ot a vacuum tube amplifier 5. The vacuum tube amplifier is well known in the art and comprises a grid, a filament and a plate, associated with which are the grid battery 6, the plate battery 7 and the filament battery 8. Associated with the grid circuit of the amplifier arethe transformers 3 and 4. The primary windings of these transformers are bridged across the lines 1 and 2 respectively, and the secondary windings thereof are connected in series in the grid circuit of the amplifier. lVhile only two transformers, such as 3 and 4, and two transmission lines, such as l and '2, have been illustrated, it is understood that the service observers set might be associated with additional lines by providing additional transformers in the manner shown. \Vhen an electromagnetic wave arrives over any one of the transmission lines such as l or 2, its voltage is applied by the corresponding input transformer, such as 3 or i, to the grid circuit of the tube 5 and is so repeated into the receiver circuit oi the observing set. The observing operator can then listen to what is taking place upon all oi the circuits at once. It is pointed out that no interference such as cross-talk can take place be tween circuits l and 2 with the arrangements of this invention as the grid circuit of the vacuum tube has a substantially infinite i1npedance and no current can Ilow through any one oi the input transformers such as 3 and 4 due to voltages set up in another of such input transformers.

The advantages of the arrangements of this invention are, in general, that one amplifier and listening set can be used simultaneously upon as many different circuits as desired. This would not be possible with the observing circuits of the prior art, which consisted essentially of a step-down trans former and receiver, because the receiver has a finite impedance and requires a finite amount of energy for its operation so that any interconnection of the secondary windings of the transformers would lead to interference, such as crosstalk, between the various circuits subject to observation.

While the arrangements of the invention have been disclosed as embodied in certain specific arrangements which are deemed dcsirable, it is understood that they are capable of embodiment in many and widely varied forms without departing from the spirit oi the invention as defined in the appended claims.

What is claimed is:

l. A plurality of transmission-lines, a circuit including receiving apparatus associated with said lines, and a unilateral vacuum bulb device in said circuit between said receiver and said lines, said device having substantially an infinite input impedance.

2. A plurality of transmission lines, a circuit including receiving apparatus associated with said lines, and a vacuum bulb amplifier having substantially an infinite input impedance in said circuit, the output circuit of said amplifier being associated with said receiving apparatus and the input circuit of said amplifier being associate with said lines.

3. A plurality of transmission lines, a circuit including receiving apparatus associated with said lines, and a vacuum bulb amplifier having substantially an infinite input impedance in said circuit, the output circuit of said amplifier being associated with said receiving apparatus and the input circuit of said amplifier being associated with said lines through a plurality of transformers, the primary winding of one of each of said transformers being bridged across one of. each of said transmission lines and the secondary windings of said transformers being connected in series in the input circuit o'l said amplifier.

4. A plurality of transmission lines, a circuit including receiving apparatus associated with said lines, and a unilateral vacuum bulb device having substantially an infinite input impedance in said circuit, the output circuit of said device being associated with said receiving apparatus and the input circuit of said device being associated with said lines through a plurality of transformers, the primary winding of one of each of said transformers being bridged across one of, each of said transmission lines and the secondary windings of said transformers being connected in series in the input circuit of said device.

5. A plurality of transmimion lines, a circuit including receiving apparatus associated with said lines, and a unilateral vacuum tube device in said circuit between said receiw'ng apparatus and said lines, said GEORGE CRISSON. 

